A linear tape file system (LTFS) as a file system for a tape drive enables data to be written and read to and from a medium from an application on an OS (Linux, Windows, Mac OS X) in units of a file. The LTFS can be used as the file system for the tape drive together with a fifth-generation linear tape open (LTO) tape drive (LTO5) and a fourth-generation IBM enterprise tape drive TS 1140. The LTFS enables a user (application) to use a tape cartridge as a high-capacity external recording medium through an operation of loading and unloading the tape cartridge as a removable medium with respect to a drive. In read and write access to the medium by the tape drive, time required for operations of unloading and loading the medium and queuing data on the medium are in units of seconds, and this deteriorates access performance.
A method generally known to reduce waiting time due to a low-speed storage includes, for example, using a high-speed storage (for example, a HDD, a flash storage) as a cache. In the case where a tape cartridge (LTFS tape) is read and written using the LTFS, this method is considered to be useful. In the case where the LTFS is used for a removable medium such as the tape cartridge, when the target medium is unloaded from a drive, the entire data on the cache is written out onto the removable medium. On this occasion, the entire data on the cache is written back onto the LTFS tape at a time. Because this write-back operation is started after the medium unload is requested, it is desirable that this write-back operation be as short as possible. In conventional use of caches, speeding-up of the write-back operation of the LTFS as the file system for the tape drive is not considered.